Lighting and radiating tube



1941- E. GERMER 2,262,177

LIGHTING AND RADIATING TUBE Filed Dec. 5, 1930 Patented Nov. 11, 19,41.

mom-mo m mums runs Edmund Germer, Berlin, Germany direct and mesnc assignments, to General Electrio Company, a corporation of New York Application December 5, 1930, Serial No. spasm In Germany December 7,1929

1 Claim.

The invention relates to a new kind of mercury vapour lamps, and more generally, to a new kind of metal vapour lamps. In ordinary lamps,

the starting of the arc is caused by contact of the liquid mercury poles. When the contact is interrupted a mercury arc starts to burn.

Now, this lamp with two liquid mercury; or

more generally metal electrodes, can be operated only on direct current. If one wants to operate the lamp by alternating current, one must use a middle tapped transformer, as is generally known, whereby the middle tap is connected to the mercury electrode, whereas the ends are connected to carbon, tungsten or nickel blocks, or sealed into the vessel, or other mercury electrodes functioning in this case as anodes only. The discharge is always uni-directional, electrons only starting from the cathode. Therefore it is necessary that the arc over-lasts the change of the current direction. Another disadvantage is that one is confined to operate such liquid metal electrode lamps at current loads of at least 1% amps. At current loads less than that limit according to the arcing point the cooling off is too rapid, and the arc will extinguish during the current change. Still another disadvantage is that the arc strikes preferably at the contact line between the mercury electrode and the wall of the vessel. This occasionally happens at higher pressure, causing cracking of the vessel if made 'of glass. Therefore, for high intensity lamps, quartz must be used instead of glass.

On the other hand, lamps have become known with solid electrodes, preferably consisting of a spiral oxide-coated and heated wire, and filled with an inert or noble gas preferably with the addition of a metal vapour such as mercury. The disadvantages with this kind of lighting or radiating tube were that one had to provide special heating means for operating the incandescent cathodes. Otherwise, such a lamp even if oxidecoated, or activated, will not start burning. Another disadvantage was that an average igniting voltage about three times as high as the ordinary operating voltage was always required. Therefore, during operation, two-thirds at least of the voltage applied will be lost in the resistance, or one has to employ a transformer with high fiux leakage coefficient, and which is rather expensive due to the comparatively high current loads for which such lamps preferably are made.

This heating of the'electrodes coupled with operation by a transformer is difficult to arrange and becomes even impossible if only direct current is available. This difference between ignitasslgnor. by

ing and operating voltages may be reduced, or the tubes length and reliability of starting may be improved at a given voltage by using special means such as auxiliary igniting anodes, or high voltage induction kicks generated by corresponding circuits as known. However, these special starting devices necessarily complicate the ar-' rangement and operation, so also there must be a plurality of lead wires for incandesclng the electrode, and a further one to apply voltage to the igniting anode at each end of the tube.

The present invention eliminates all these complications or disadvantages and concerns a tube, which requires only one lead wire on each end, and will start burning at the application of only a low voltage, even at the application of the usual distribution voltage.

This progress has been achieved by using a special kind of electrode, by filling with rare gasses at special pressures depending on the dimensions of the tube, and by the provision of a certain amount of metals at definite places inside the tube.

By applying these and other means which will be described in detail in the following, a process of igniting and burning of the lamp is brought about which may be described as a self heating glow point cathode.

Directly upon application of low voltage, a glow discharge occurs, and this discharge has a special characteristic: it does not start from the cathode surface evenly and uniformly as in the case of bare metal cathodes or metal cathodes covered with a film ofactivated alkaline metals. 0n the contrary, it starts from quickly moving little glowing points, due to the provision of heat concewtrating means as constituents of the electrodes. These glow points are transferred rapidly into one or more arcing points, and the glow discharge is then transformed into an arc of several amperes, or more. The increase in current load of the tube will increase the vapour pressure, owing to the presence of easily vaporizing metal in the tube to such an extent that this metal vapour takes over the current conductionand light emission within a few seconds. Furthermore, the dimensions of the tube, the heat losses by radiation and conduction on the one hand, and on the other hand theheat generation by voltage consumption in the arc path and at the electrodes, depending on the amount'of series resistance, may be adapted so that the vapour pressure exceeds by far the pressure ranges common in incandescent activated cathode tubes. The lamp thereby will operate so that the arc consumes an ever increasing portion of the total voltage applied, up to more than two-thirds of this voltage, as compared with only about onethird in the low pressure tubes.

Hereinafter the invention as well as the method of obtaining the result may be described in a more detailed manner, by reference to the ac- I drawing, or examples, and any useful changes, omissions or additions may be made within the limits and the scope of the claim.

In Figure 1, l is the tube proper with two electrode containers, 2 and 3 at the ends into which are sealed the electrodes 4 and 5. 6 indicates three or four thick turns of electrode material which consists of metal gauze, mesh or twisted wires or ribbons of nickel or other suitablemetal not in the form of a filament but in a more compact unit, and secondly, of a filling or coating mass consisting of the activating material. This electrode body proper 8 is inserted into a ring 'I of heavy wire andthis in its turn is mounted on a frame 8, which is carried by a lead wire 9. Instead of the ring 1 there may be used a slotted disc III as shown the right hand cathode in this figure, at the edge of which is affixed the intermingled wire or ribbon body 6. Instead of using the frame 8 the lead wire 9 may be directly welded to the ring or the disc. The intermingled wire mass called hereinafter the cathode or electrode body proper has a porous absorbent structure filled up with the activating material. By applying a high frequency coil around the electrode container the ring or the disc which forms a short circuit will receive a large amount of high frequency energy, and the eddy current which will not suffer much loss in the ring or disc which is made appropriately thick, will heat the electrode body proper to a high temperature for degassing it as heating the barium oxide is mostly reduced by contact with the nickel structure or by dissociation, whereas the last mentioned compounds will be only slightly affected. In consequence, all the mass left is soaked with free barium, and complex compounds formed of barium. I have used the word activated herein to describe electrodes having electro positive material added to the more refractory conductive carrier to increase the electronic emission of the electrode. A depression l', situated near the middle of the length of the tube in the shown example takes up the necessary quantity of mercury or other vaporisable metal.

For obtaining the necessary pressure of the mercury vapour and thus an arc it is important that the dimensions of the tube and the elec-- trodes have proper proportion. Incorrect proportions may result in excessive cooling, in which case high pressure cannot be attained since the excessive energy input which would be necessary to maintain high pressure would destroy the electrodes; or if the tube is too small it may get too hot with a current loading sufflcient to establish and maintain the arcing' points on the electrode. The following is an example of dimensions of a practical and economical lamp. The distance between both electrodes amounts to 350 m. m., the channel has an inside diameter of 20 m. m., the pole vessels about 28 mm. The tube may be made of quartz or of a glass permeable for ultra violet rays. The dimension. of the electrode in this case are given by the following data: it consists of 20 twisted nickel wires each of 0.35 m. m. diameter, wound to a spiral of 5 steps with an outer diameter of about 8 m. m. The space between two windings is less than 1 m. m. This proper electrode is welded to a frame support of a nickel wire of 3 m. m. diameter flattened under the hammer to a thickness of about 1% to 2 m. in. With these dimensions the lamp starts to burn at 6 amps,-

of about 120 .volts and accordingly at a current of about 3.2 amps. From the said proportions the dimensions may differ up to 30 percent positively as well as negatively.

This tube operates as follows. Upon the application of a voltage along the tube, a glow discharge arises from points of suitable or higher free barium concentration, which form visible glowing points. By the surrounding heat concentrating materials these points are rapidly transformed into arcing points, from which under a reduced cathode drop of only few volts an arc starts which replaces the previous glow discharge.

On application of alternating voltages each electrode functions alternately as cathode and anode. In operation with direct current only one of the electrodes needs to be of the previously described types. However, the first mentioned type of lamp with two such electrodes may be used satisfactorily in all cases. By determining the thickness of the ring I or disc I0 correctly any superfluous anodic heat is conducted away and dissipated.

To obtain a discharge at all in a cold lamp,

- the lamp must contain a conductive atmosphere already in the cold state when it is put on voltage and before the metals are vaporised.

This is achieved by filling the tube with an inert or rare gas such as neon or especially argon at a suitable pressure, which depends on the dimension of the tube and which is rather critical for given dimension, thus with a tube as described above argon needs to be used at a pressure of 1.5 m. m. mercury column, or neon at a pressure of 4 to 9 m. m., corresponding to tube dimensions as described of about 20 m. m. in diameter, and 250 m. m. length, and a supply line I voltage of about 220 volts.

are connected to the anode and extend into the 4 nearest proximity of the cathode. In the case of alternating current operation such a conductive layer is only connected with one electrode and extends into the neighbourhood of the other. One can secure this by making a uniform conductive streak from one electrode to the other, and interrupting it near the one electrode by a narrow slot. This is the most emcient arrangement. The conductive layer extends over as large a part of the surface of the tube as possible. -It may consist of a metallic layer which reflects the generated light to a good degree. This conductive layer on application of voltage causes a voltage drop to arise between it and the other electrode or the small portion of conductive layer connected with the latter which voltage drop also between the electrodes proper produces a feeble glow discharge which subsequently transforms itself into an arc. The voltage drop depends on the distance of the electrodes and is initially 20 to 50 volts corresponding to distance of 20 to 70 centimetres.

Figure 2 shows a specially useful arrangement. This is a U- or V-shaped lamp which is operated in a vertical position as shown in the figure with the electrodes uppermost. The metal, especially mercury, is placed at the lowest point of the lamp, preferably in a depression I! of the tube proper. There it is heated by the discharge which causes a continual beam of mercury vapour to be blown into the direction to the electrodes, l and 5. Any materials such as nickel and barium, sputtered or vaporised from the cathode, are therefore hindered to migrate into the tube proper I. Instead of this, they are repulsed and blown back into the electrode container. The mercury beam is condensed there on the wall, and the sputtered metal is condensed there as well. The mercury itself will run down to the aforementioned pool in little globules, whereas the nickel and other impurities remain in the electrode container. The tube part which is supposed to give of! the lighting or ultra violet radiation remains clean and free from blackenins.

To improve this action the electrode container and the tube proper are separated by restricted portions l3 and H, or by several such restrictions.

The electrodes are surrounded by special cylinders i5 and it, provided inside of the cathode container. I'hese cylinders may be fused to the upper or to the main part of the container, or to the lead and carrier wire of the electrode, or they may be fastened in any other suitable manner. Thereby materials evaporating from the cathode will be intercepted by the cylinder and settle on its inner wall, whereas the mercury stream will not condense inside of this cylinder because of the proximity of the electrode and the high temperature, but on the inner wall of the container. As the mercury and the nickel etc. are condensing at different places, the mercury will not wash out the deposited nickel, barium, etc., whereby the mercury would be spoiled and the tube blackened. The cylinder may consist of glass, quartz, or any other suitable material. The shape of a U or V is of course not the only one possible, on the contrary, there are various forms in which a mercury vapour stream is directed against the electrodes or electrode containers and the condensed mercury allowed to run back into the tube proper.

The electrode carrier and seal wire as it is known in the art may be sealed in the usual way into the container. Also there may be used instead a metal cone put into a ground and fitting socket provided in the body'of the container and made vacuum tight by mercuryas known from the quartz lamp of the Quartzlampeni'abrik at Hanan (Germany). Still another way of making an air tight sealing, especially to the quartz which is very difllcult to handle, is shown in the drawing. The lead wire 9 is fused into a rather thick walled quartz tubing H, which in its turn is fused to the container at the upper part of the main quartz .tubing, and there is provided a cup it which is filled with any suitable vacuum tight material such as sealing wax, or the like.

When the tube is put in operation the metal is soon vaporised and takes over the current conduction and light emission, and as this takes place the arc column is constricted until, instead of filling the entire tube as in the first moment after starting, the luminous cord is contracted away from and is much narrower in diameter than the tube, e. g., less than one-half. However, the useful operating voltage across the tube as compared with the igniting voltage is rather low in all these gas filled incandescent cathode tubes. Now the tube dimensions on the one hand and the series resistance on the other are chosen so that the current load determining the heat development is so large that the metal vapour pressure will be considerable, even remarkably over atmospheric pressure. According to the invention the tube may be operated at such a pressure that the voltage drop after it has fallen down at the moment of ignition to 20 to 40 volts will increase again and reach to volts if 220-260 volts at least are applied. This means that only one-third of the total voltage applied is consumed in the series resistance. "Besides this the light and ultra violet radiating economy per watt consumed in the arc will be twice that of the low pressure tube working at medium pressures, and three to four times as high at a vapour pressure about one atmosphere.

A lamp as described may be used for lighting purposes as well as special for ultra violet radiation purposes. filled with mercury, whereas for lighting other metals, especially such as thallium, gallium, alkaline metal, etc. can be used. The lamps may be operated at low as well as preferably at high pressures. At any pressure they will burn reliably at amp. as well as at 10 and more amps.

For the smaller types of lamps up to 1.5 amps. current input it is advisable to insulate part of the tube against heat transmission. This may be done for example by covering the lower part of the electrode container with heat insulating materials such as asbestos, or by insulating the reverse part of the whole tube against heat removal.

For ultra violet radiation purposes it is advisable to make use of the heat and infra-red radiation from the series resistance. To this behalf the resistance preferably is arranged in the same reflector, so that heat and infra-red rays are directed in the same direction as the ultra violet output.

For signalling, advertising, and similar purposes, use may be made of the property of the lamp that depending on the amount of the series resistange connected the vapour pressure will be allowed to exceed the working point of the lamp, so that the arc is blown out. On subsequent cooling it will then re-ignite, and this will be repeated, the lamp alternately extinguishing and igniting at definite and easily adjustable time periods.

In the latter case it must be- I claim:

In an arc discharge device the combination of a thermionic electrode subject to disintegration by-the action of the discharge and a shield of reiractm'y material surmunding said electrode but spaced therefrom and from the discharge and not electrically connected in said electrode ther from the discharge adapted to dissipate 5 heat from said constriction.

EDMUND GERMER.

CERT IFIGA'I'E OF CORRECTION Patent No. 2,252,177. November 11, 19m.

EDMUND GERMER.

It is hereby certified that error appears in the printed specification of the abovenumbered patent requiring correction as follows: Page 2, second column, line 65, after "1.5" insert -to 5"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed am sealed this 21st day of July, A. D. 19!;2.

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.

, cmumic m' OF CORRECTION.

Patent No. 2,252,177. November 11, 19141.

-EDHUND GERMER It is hereby certified that error eppears in the printed specification of the above-numbered patent requiring correction as follows: Page 2, second column, line65, after "1.5" insert -to 5-; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed m1 sealed this 21st day of July, A. D. 19h2.

7 Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

